You can integrate 30% or smaller wireless keyboard (with Elite-C) in your trousers IMHO. This would address "good" part (think something like this https://www.tzcl.me/blog/rae-dux but without PCB and wired using wires). At least I use adux keyboard of similar size daily. Or you can go even smaller with something like this https://artsey.io/ but I am not sure if this could be considered good. Next part would be concealing it - kailh low profile are too high IMHO for pants. There are switches that are even lower but most probably this might not work. I guess captive touch sensors might be solution but I am not sure if they would work well as keyboard. I guess some art would help concealing as well.

Still I don't feel this would be really comfortable to type on.